Since the period of rapid economic growth, a number of suburban housing subdivisions have been developed for the steadily increasing population in Japan. As new towns are developed, new people and families come to live there, and new relationships begin in the neighborhood.

Such a style of Japanese society has changed over a long time, and neighborly ties are weakening. This phenomenon is said to be observed not only in metropolitan areas but also in suburban housing subdivisions in rural areas.

However, the importance of local communities based on such neighborly ties has been increasingly revalued since the Great East Japan Earthquake in March 2011.

There is a large-scale solar power plant constructed next to such a suburban housing subdivision in a rural city. It is “Ise Futami Mega Solar Hikari no Machi (town of light),” which was constructed by Sanko Real Estate Co Ltd. (Tsu City, Mie Prefecture), a subsidiary of Mie Kotsu Group Holdings Inc. (Fig. 1 & 2). Sanko Real Estate has been developing real estate primarily along the bus routes run by Mie Kotsu.

Constructed in commercial zone in housing subdivision

“Hikari no Machi,” the housing subdivision adjoining this solar power plant, is located on a hill, about a 10-minute drive from JR Futamiura Station. Land purchase started in the 1970s and the sale of housing lots started in 1997 with a total of 606 lots prepared. As of today, about 300 lots are occupied.

From the beginning of the development, it was planned that the houses would be built on the north side of the housing subdivision and commercial facilities serving the residents would be built in the remaining 10ha on the south side. Candidate facilities included a hospital and supermarket; however, the south side has been left idle as no firm has ever wanted to move in.

What changed this situation was the Great East Japan Earthquake. Power shortages became a reality in the service area of Tokyo Electric Power Company (TEPCO), and the feed-in tariff (FIT) system for renewable energy started amid the highest-ever interest in energy.

Is it possible to construct a service facility that supplies power to support one of the basic elements of human life and use it as a reserve power supply for emergencies in the local community while selling electricity during usual conditions? Moreover, on the south side of Hikari no Machi is the wide-area disaster prevention base of Mie Prefecture.

Partly because Mie Prefecture’s Governor Eikei Suzuki was responsible for renewable energy at the Ministry of Economy, Trade and Industry, he had strong feelings about energy issues and declared, “Mie Prefecture will lead the promotion of renewable energies,” which, as a result, facilitated the solar power plant project in Hikari no Machi.

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Generated power preferentially used to charge batteries

The equipment to house and charge secondary batteries was set up next to the entrance to this solar power plant, which has 5.2MW of maximum output. The aim is to enable the residents of the adjoining housing subdivision to be able to immediately use the batteries should a disaster strike. Small-type 2.2kW secondary batteries were chosen to be housed so the residents could carry them on bicycles.

In light of such a purpose, the key of the charger and the housing apparatus is kept by the chairman of the residents’ association. The generated power is programmed to be preferentially used to charge these secondary batteries even during usual conditions.

For the secondary batteries, a PV inverter with 50kW-rated output, which is rare at a large-scale solar power plant, was introduced. It is a home-use PV inverter manufactured by GS Yuasa Corp. The reason for its introduction is that the PV inverter is a stand-alone type that keeps on operating even if the power system network goes down at the time of a disaster.

Industrial PV inverters are designed to stop operating when the connected power system goes down. Therefore, such a PV inverter was necessary apart from the other industrial PV inverters in the plant.

In addition to this PV inverter for secondary batteries, 500kW and 250kW PV inverters manufactured by Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) are used in combination to generate power for sale under usual conditions.

Sept 1, 2013, or the first National Disaster Prevention Day since this solar power plant started generating electricity, an outdoor cooking test-run using the secondary batteries charged by the plant was included in the list of regular disaster drills conducted by the residents’ association of the adjoining housing subdivision (Fig. 3 & 4).

Those disaster drills are conducted by the residents of the housing subdivision, instead of Sanko Real Estate, which is responsible for the subdivision’s management and operation. Although it is a recent housing subdivision where neighboring ties are weakening, events such as a summer festival, traditional dances and disaster drills have been conducted by enthusiastic residents in Hikari no Machi since its early days. And a strong local community has been formed through those activities.

An attempt to charge and use the secondary batteries with the electricity generated at the solar power plant was also made in the disaster drills. Solar power generation has started to be accepted by the local community.

In addition, Sanko Real Estate’s Information Center in the southernmost part of the subdivision to the north of the solar power plant is being used as an environmental studies room. Groups of people such as classes from elementary/junior high schools and corporate parties visit almost every week.

“Following the opening of this solar power plant, the town became more linked to this subdivision’s name, “Hikari no Machi (town of light),” said Michitaka Nakamura, director of the General Planning Department and manager of the Environmental Energy Operation, Sanko Real Estate, outlining his expectation for synergies to be formed.

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Stable power generation even with little sun

Sanko Real Estate tried to construct this solar power plant by itself as much as it could without relying on consultants and others.

“Despite the difference between offices/condominiums and power plants, real estate companies are suited to plant construction because they can leverage expertise established through real estate development relatively well,” Nakamura said.

The deployed solar panel is the CIS solar cell manufactured by Solar Frontier K.K. Approximately 32,300 panels are installed. One of the factors behind the deployment was praise for the product’s reputation from another power producer who had earlier adopted the same panel. According to this source, the amount of generated power greatly outperformed the estimate indicated by the manufacturer.

“Despite our concern for the unusual adoption of CIS solar cells by 5MW-class plants, the amount of power generation has outperformed our expectations by more than 30%,” Nakamura said.

CIS solar panels are said to be superior in their amount of power generation during hours with little sunshine, such as the morning, late afternoon and cloudy days.

The output linearly rises toward peak hours with conventional crystalline silicon solar cells. With CIS solar cells, on the other hand, the output gradually rises toward peak hours. And it lowers little even when the output is low, which, as a result, leads to higher output compared with crystalline silicon solar cells.

As this feature makes a significant difference in Japan, where the amount of solar irradiation is limited and days and hours of power generation at peak output are also limited, CIS solar panels are expected to make it easy to secure a certain amount of power generation during the period from fall to spring.

Chiyoda Corporation designed and constructed the plant. Operation and maintenance is undertaken by Sanko Community, a 100% subsidiary of Sanko Real Estate, which is engaged in building/condominium maintenance, security and management.

Excluding GS Yuasa’s product for secondary batteries, the PV inverters used at the plant are TMEIC products. Sanko Real Estate initially planned to deploy a 1,000kW PV inverter manufactured by ABB of Switzerland, but changed its supplier to TMEIC due to various reasons including their reliability and support services.

The construction cost was reduced from the initially announced ¥2 billion (approx US$20.3 million) to about ¥1.6 billion. Of the ¥1.6 billion, about ¥1.2 billion is the cost of power generation facilities, and ¥400 million was used for land reclamation, etc.

PV inverters arranged in view of subdivision residents

The solar power plant faces south with a river running on the south side. In other words, the location is suited for a large-scale solar power plant because it allows to take in sunlight under good conditions and is free from concerns about buildings being built nearby that block the panels from sunshine.

The solar panels are set up about 70cm from the ground, tilted at 10°. According to Sanko Real Estate, the height and angle were optimum for the well-balanced intensity, cost and convenience for constructing the mounting system.

At this height and angle, the posts of the mounting system can be made short, and, as a result, constructors can set up the solar panels without using a stepladder, etc (Fig. 5). The mounting system is designed assuming wind speeds of up to 36m.

What is unique about this solar power plant’s design is the PV inverters positioned together in the center of the solar panels, which are neatly arrayed according to a grid system (Fig. 6). This represents consideration given to the residents of the adjoining subdivision who are concerned about operating noise and electromagnetic waves from the PV inverters. Positioning the PV inverters in the center of the plant also reduces the length of cable that connects the solar panels and PV inverters.